Add video to migrate an existing app

Author: ericbrown99

docs/mini-apps/quickstart/migrate-existing-apps.mdx

@@ -2,6 +2,17 @@
 title: Migrate an Existing App
 description: Quickly migrate your existing app to a mini app, preview it in Base Build, and publish to the Base app.
 ---
+<Panel>
+<iframe
+  className="w-3/4 aspect-video rounded-xl mx-auto block"
+  src="https://www.youtube-nocookie.com/embed/bChuIvqLiX0"
+  title="Turning an Existing App into a Mini App on the Base App"
+  frameBorder="0"
+  allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture"
+  allowFullScreen
+></iframe>
+</Panel>
+
 **Prerequisites** 
 * You have an existing web app 
 * You have a Base app account